Pass false as the 2nd argument to class_exists() to disable autoloading and to not cause problems for those who define __autoload().

Fixes #20523.


git-svn-id: https://develop.svn.wordpress.org/trunk@34348 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/wp-db.php

@@ -2993,10 +2993,11 @@ class wpdb {
 	 */
 	public function bail( $message, $error_code = '500' ) {
 		if ( !$this->show_errors ) {
-			if ( class_exists( 'WP_Error' ) )
+			if ( class_exists( 'WP_Error', false ) ) {
 				$this->error = new WP_Error($error_code, $message);
-			else
+			} else {
 				$this->error = $message;
+			}
 			return false;
 		}
 		wp_die($message);